An optical imaging apparatus which irradiates a living body with light and which images information on an inside of the living body obtained in accordance with the incident light has been actively researched in a medical field. An example of such an optical imaging technique includes photoacoustic tomography (PAT). In photoacoustic tomography, a living body is irradiated with pulsed light generated from a light source so that acoustic waves generated from body tissues which absorb energy of the pulsed light which is propagated and dispersed in the living body are detected. One example of such a technique is described in U.S. Pat. No. 5,840,023 entitled “Optoacoustic Imaging for Medical Diagnosis” (hereafter “Patent Literature 1”). Specifically, elastic waves, that is, photoacoustic waves, generated when a detection target absorbs the irradiated light energy and therefore is momentarily expanded are received by a transducer by utilizing a difference between an optical energy absorption rate of the detection target such as a tumor and optical energy absorption rates of other tissues. By performing analysis processing on the detection signals, an optical characteristic distribution, and especially, an optical-energy absorption density distribution are obtained. This information may be used for quantitative measurement of a specific substance included in the inspection target such as glucose and hemoglobin included in blood, for example. Accordingly, the photoacoustic tomography may be utilized to specify a portion which includes a malignant tumor and growing new blood vessels.
Furthermore, Lihong V. Wang in “Tutorial on Photoacoustic Microscopy and Computed Tomography” (hereafter “Non Patent Literature 1”) discloses an example of a case where a photoacoustic microscope is employed for photoacoustic imaging (PAI). According to Non Patent Literature 1, ultrasonic waves obtained by irradiating an inspection target with pulsed light are received by a transducer which performs imaging. Furthermore, by changing a wavelength of the pulsed light, spectroscopic characteristics of the inspection target are imaged.